Communication system

ABSTRACT

The communication system includes a first communication device, a second communication device, and a third communication device. The first communication device outputs a high frequency alternating current power, and a power receiving circuit of the second communication device receives the high frequency alternating current power via a second antenna. A power line is connected between the second antenna and the power receiving circuit. A first power line has a first semicircle portion and a second power line has a second semicircle portion. The first and second semicircle portions are combined together to provide a loop-shaped antenna. The third communication device receives the high frequency alternating current power output from the loop-shaped antenna. At least two of the first, second, or third communication devices transmit or receive communication signals using respective antennas. The first and second power lines are twisted with each other at a portion other than the loop-shaped antenna.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on Japanese Patent Application No. 2012-212471filed on Sep. 26, 2012, the disclosure of which is incorporated hereinby reference.

TECHNICAL FIELD

The present disclosure relates to a communication system includingmultiple communication devices that communicate with one another.

BACKGROUND ART

In a conventional power supply system, a power source outputs a highfrequency alternating current power to a power line and multiplecommunication devices wirelessly receive the high frequency alternatingcurrent power from the power line (for example, refer to PatentLiterature 1).

Further, a communication system includes parallel power supply linesthrough which communication signals propagate and a pickup device thatreceives the communication signals from the parallel power supply linesvia a coupling device (for example, refer to Patent Literature 2).

Based on the systems disclosed in above-described Patent Literature 1and Patent Literature 2, the inventors of the present disclosure studiedon a communication system having a power line and a communicationdevice. In this communication system, the power line transfers asuperposition of high frequency power and a communication signal, andthe communication device receives the high frequency power and thecommunication signal via a coupling device in a electromagneticinduction manner. After the study on this communication system, theinventors of the present disclosure found that a part of the highfrequency alternating current power and the communication signals leakas electromagnetic waves at a portion other than the coupling device.

PRIOR ART LITERATURES Patent Literatures

[Patent Literature 1] WO 2007/029438 A1

[Patent Literature 2] JP 2005-45327 A

SUMMARY OF INVENTION

In view of the foregoing difficulties, it is an object of the presentdisclosure to provide a communication system that suppresses a leakageof high frequency alternating current power and communication signalsfrom a power line.

According to an aspect of the present disclosure, a communication systemincludes a first communication device, a second communication device, apower line, and a third communication device. The first communicationdevice includes a first antenna that outputs a high frequencyalternating current power. The second communication device includes asecond antenna and a power receiving circuit, and the power receivingcircuit receives, via the second antenna, the high frequency alternatingcurrent power output from the first antenna. The power line is connectedbetween the second antenna and the power receiving circuit. The powerline includes a first power line, which is positioned between apredetermined portion of the power line and the second antenna, and asecond power line, which is positioned between the predetermined portionof the power line and the power receiving circuit. The first power lineincludes at least one first semicircle portion having a semicircleshape, and the second power line includes at least one second semicircleportion having a semicircle shape. The at least one first semicircleportion and the at least one second semicircle portion are combinedtogether to provide at least one loop-shaped antenna. The thirdcommunication device includes a third antenna, which receives, via thethird antenna, the high frequency alternating current power output fromthe at least one loop-shaped antenna. At least two of the firstcommunication device, the second communication device, or the thirdcommunication device transmit or receive communication signals viacorresponding antennas. The first power line and the second power lineare twisted with each other to configure a twisted line pair at aportion other than the at least one loop-shaped antenna in the powerline.

In the above system, the power line has the twisted line pair, which isconfigured by the first power line and the second power line, at aportion other than the loop-shaped antenna. Thus, a leakage of the highfrequency alternating current power and the communication signals from aportion other than the loop-shaped antenna can be suppressed.

BRIEF DESCRIPTION OF DRAWINGS

The above and other objects, features and advantages of the presentinvention will become more apparent from the following detaileddescription made with reference to the accompanying drawings. In thedrawings:

FIG. 1 is a diagram showing an electric configuration of a vehicularcommunication system according to an embodiment of the presentdisclosure;

FIG. 2 is a diagram showing an operation of the vehicular communicationsystem according to the above embodiment;

FIG. 3 is a graph showing a relation between a radius of a loop-shapedantenna and a space transfer efficiency;

FIG. 4 is a diagram showing a relation between a distance and a spacetransfer efficiency; and

FIG. 5A and FIG. 5B are diagrams each of which showing a dimension ofthe power line and a dimension of the antennas according to the aboveembodiment.

EMBODIMENTS FOR CARRYING OUT INVENTION

The following will describe embodiments of the present disclosure withreference to the drawings. FIG. 1 shows an electric configuration of avehicular communication system 1 according to an embodiment of thepresent disclosure.

The vehicular communication system 1 according to the present embodimentincludes a communication device 10 as a master and communication devices20, 30, 40 as slaves. The vehicular communication system 1 operates in amaster-slave manner.

The communication device 10 includes a communication circuit (COMM CIRC)11, an antenna 12, and a power supplying circuit (PW SP CIRC) 13. Thecommunication circuit 11 transmits or receives a communication signalvia the antenna 12. In the present embodiment, the antenna 12 isprovided by a coil-shaped antenna. The power supplying circuit 13outputs a high frequency alternating current power to the antenna 12 inorder to supply the electric power to the communication devices 20, 30,40, 50.

The communication device 20 includes a communication circuit (COMM CIRC)21, an antenna 22, and a power receiving circuit (PW RC CIRC) 23. Thecommunication circuit 21 transmits a communication signal via theantenna 22, and receives a communication signal via the antenna 22. Inthe present embodiment, the antenna 22 is provided by a coil-shapedantenna.

In the antenna 22, one electrode 22 a is connected with thecommunication circuit 21 and the power receiving circuit 23, and theother electrode 22 b is connected with the communication circuit 21 andthe power receiving circuit 23 via the power line 60. With thisconfiguration, the power line 60 is connected between the powerreceiving circuit 23 and the antenna 22. The power line 60 supplieselectric power to the communication devices 20, 30, 40, and providesloop-shaped antennas 61, 62, 63. Details of the power line 60 will bedescribed later.

The power receiving circuit 23 receives, via the antenna 22, the highfrequency alternating current power output from the antenna 12. Thepower receiving circuit 23 converts the high frequency alternatingcurrent power to a direct current power and supplies the converteddirect current power to the communication circuit 21 and other electricloads.

The communication device 30 includes a communication circuit (COMM CIRC)31, an antenna 32, a power receiving circuit (PW RC CIRC) 33, a powerstorage circuit (PW ST CIRC) 34, a power transfer circuit (PW TR CIRC)35, and a disconnection detection circuit (DETC CIRC) 36. Thecommunication circuit 31 receives a communication signal from theloop-shaped antenna 61 via the antenna 32, and outputs a communicationsignal to the loop-shaped antenna 61 via the antenna 32. In the presentembodiment, the antenna 32 is provided by a coil-shaped antenna(receiving coil).

The power receiving circuit 33 receives the high frequency alternatingcurrent power from the loop-shaped antenna 61 via the antenna 32, andconverts the high frequency alternating current power that is receivedto a direct current power. Then, the power receiving circuit 33 outputsthe direct current power to the power storage circuit 34. The powerstorage circuit 34 stores the direct current power to a battery or to acapacitor. The power transfer circuit 35 converts the direct currentpower stored in the power storage circuit 34 to a high frequencyalternating current power, and transfers the high frequency alternatingcurrent power to the loop-shaped antenna 61 via the antenna 32. Thedisconnection detection circuit 36 detects a disconnection between thecommunication device 10 and the communication device 30 based on acommunication state between the two communication devices 10, 30.

The communication device 40 includes a communication circuit (COMM CIRC)41, an antenna 42, and a power receiving circuit (PW RC CIRC) 43. Thecommunication circuit 41 transmits a communication signal to theloop-shaped antenna 62 via the antenna 42, and receives a communicationsignal from the loop-shaped antenna 62 via the antenna 42.

In the present embodiment, the antenna 42 is provided by a coil-shapedantenna (receiving coil).

The power receiving circuit 43 receives, via the antenna 42, the highfrequency alternating current power output from the loop-shaped antenna62. The power receiving circuit 43 converts the received high frequencyalternating current power to a direct current power, and supplies theconverted direct current power to the communication circuit 41 and otherelectric loads.

The communication device 50 includes a communication circuit (COMM CIRC)51, an antenna 52, and a power receiving circuit (PW RC CIRC) 53. Thecommunication circuit 51 transmits, to the loop-shaped antenna 63, acommunication signal via the antenna 52, and receives, from theloop-shaped antenna 63, a communication signal via the antenna 52. Inthe present embodiment, the antenna 52 is provided by a coil-shapedantenna (receiving coil).

The power receiving circuit 53 receives, via the antenna 52, the highfrequency alternating current power output from the loop-shaped antenna63. The power receiving circuit 53 converts the received high frequencyalternating current power to a direct current power, and supplies theconverted direct current power to the communication circuit 51 and otherelectric loads.

The electric load of the communication device 20 is greater than anelectric load of each other communication device 30, 40, 50. Thecommunication device 20, 30, 40, or 50 may include, for example, anactuator of a servomotor of a vehicle air conditioning apparatus as theelectric load.

In the present embodiment, the power line 60 is folded at a longitudinalintermediate portion 60 a toward the antenna 22 (toward the powerreceiving circuit 23). The power line 60 transfers a superposition ofthe high frequency power and the communication signal. The transferoperation will be described later in detail.

As described above, the power line 60 is connected between the powerreceiving circuit 23 and the antenna 22.

In the power line 60, a segment positioned between the intermediateportion 60 a and the antenna 22 provides a first power line. The firstpower line includes semicircle portions 61 a, 62 a, 63 a. The semicircleportions 61 a, 62 a, 63 a are distant from one another.

In the power line 60, a segment positioned between the intermediateportion 60 a and the power receiving circuit 23 (or the communicationcircuit 21) provides a second power line. The second power line includessemicircle portions 61 b, 62 b, 63 b. The semicircle portions 61 b, 62b, 63 b are distant from one another.

In FIG. 1, a bold black line (filled in black) indicates the first powerline, and a white line (hollow line) indicates the second power line.

A combination of the semicircle portions 61 a and 61 b provides theloop-shaped antenna 61. A combination of the semicircle portions 62 aand 62 b provides the loop-shaped antenna 62. A combination of thesemicircle portions 63 a and 63 b provides the loop-shaped antenna 63.

The following will describe an operation of the vehicular communicationsystem 1 according to the present embodiment with reference to FIG. 2.

First, the communication device 10 starts a transmission of the power(step S100). Specifically, the power supplying circuit 13, via theantenna 12, outputs the high frequency alternating current power. Thehigh frequency alternating current power is output from the antenna 12as electromagnetic waves to the antenna 22. After the high frequencyalternating current power is received by the antenna 22, a part of thehigh frequency alternating current power is supplied to the powerreceiving circuit 23. That is, the communication device 20 receives theelectric power (step S100). Specifically, the communication device 20receives the high frequency alternating current power from thecommunication device 10 in high power.

As described above, a part of the high frequency alternating currentpower received by the antenna 22 is supplied to the power receivingcircuit 23, and remaining part of the high frequency alternating currentpower is output to the loop-shaped antenna 61, 62, 63 as electromagneticwaves via the power line 60.

The power receiving circuit 33 receives, via the antenna 32, the highfrequency alternating current power from the loop-shaped antenna 61.That is, the communication device 30 receives the electric power (stepS120). Then, the power receiving circuit 33 converts the high frequencyalternating current power, which is received via the antenna 32, to thedirect current power, and supplies the direct current power to the powerstorage circuit 34. Then, the power storage circuit 34 stores the directcurrent power (step S130).

The power receiving circuit 43 receives, via the antenna 42, the highfrequency alternating current power from the loop-shaped antenna 62.That is, the communication device 40 receives the electric power (stepS140). The communication device 40 receives the high frequencyalternating current power from the communication device 10 in low power.

The power receiving circuit 53 receives, via the antenna 52, the highfrequency alternating current power from the loop-shaped antenna 63.That is, the communication device 50 receives the electric power (stepS140). The communication device 50 receives the high frequencyalternating current power from the communication device 10 in low power.

As described above, the communication device 10 supplies the highfrequency alternating current power to the communication devices 20, 30,40, 50.

The communication device 10 also communicates with the communicationdevices 20, 30, 40, 50.

Specifically, the communication circuit 11 of the communication device10 outputs call signals for calling each of the communication devices20, 30, 40, 50 at predetermined intervals. The communication circuit 11outputs the call signals via the antenna 12 as electromagnetic waves.The communication circuit 21 of the communication device 20 receives thecall signals via the antenna 22.

In response to the reception of the call signals, the communicationcircuit 21 of the communication device 20 outputs, via the antenna 22,response signals to the antenna 12. The communication circuit 11 of thecommunication device 10 receives the response signal via the antenna 12.

The call signals received by the antenna 22 are transmitted via thepower line 60, and are output by the loop-shaped antennas 61, 62, 63.

For example, the communication circuit 31 receives, via the antenna 32,the call signal output from the loop-shaped antenna 61. Then, thecommunication circuit 31 outputs a response signal via the antenna 32.When the loop-shaped antenna 61 receives the response signal from thecommunication circuit 31, the loop-shaped antenna 61 transmits theresponse signal to the antenna 22 via the power line 60, and the antenna22 outputs the response signal to the antenna 12. Then, thecommunication circuit 11 receives the response signal, which is outputfrom the communication 31, from the antenna 12.

For example, the communication circuit 41 receives, via the antenna 42,the call signal output from the loop-shaped antenna 62. Then, thecommunication circuit 41 outputs a response signal via the antenna 42.When the loop-shaped antenna 62 receives the response signal from thecommunication circuit 41, the loop-shaped antenna 62 transmits theresponse signal to the antenna 22 via the power line 60, and the antenna22 outputs the response signal to the antenna 12. Then, thecommunication circuit 11 receives the response signal, which is outputfrom the communication 41, from the antenna 12.

For example, the communication circuit 51 receives, via the antenna 52,the call signal output from the loop-shaped antenna 63. Then, thecommunication circuit 51 outputs a response signal via the antenna 52.When the loop-shaped antenna 63 receives the response signal from thecommunication circuit 51, the loop-shaped antenna 63 transmits theresponse signal to the antenna 22 via the power line 60, and the antenna22 outputs the response signal to the antenna 12. Then, thecommunication circuit 11 receives the response signal, which is outputfrom the communication 51, from the antenna 12.

The disconnection detection circuit 36 of the communication device 30monitors a disconnection state (specifically, a disconnection statebetween the antenna 22 and the loop-shaped antenna 61 in the power line60) of the power line 60 (step S140).

For example, when the call signals transmitted from the communicationdevice 10 are received by the communication circuit 31 at predeterminedintervals, the disconnection detection circuit 36 determines that nodisconnection occurs in the power line 60 between the antenna 22 and theloop-shaped antenna 61.

For example, when the call signals transmitted from the communicationdevice 10 are failed to be received by the communication circuit 31 fora predetermined period, the disconnection detection circuit 36determines an occurrence of the disconnection in the power line 60between the antenna 22 and the loop-shaped antenna 61.

When the disconnection detection circuit 36 determines an occurrence ofthe disconnection in the power line 60, the disconnection detectioncircuit 36 controls the power transfer circuit 34 to output the directcurrent power stored in the power storage circuit 34 as a high frequencyalternating current power via the antenna 32 (step S150). The highfrequency alternating current power output via the antenna 32 isreceived by the loop-shaped antenna 61. The high frequency alternatingcurrent power received by the loop-shaped antenna 61 is transferred toother loop-shaped antennas 62, 63. Then, the loop-shaped antennas 62, 63provide the high frequency alternating current power transferred fromthe loop-shaped antenna 61 to the communication devices 40, 50.

The power receiving circuit 43 receives, via the antenna 42, the highfrequency alternating current power output from the loop-shaped antenna62. That is, the communication device 40, which is directly coupled withthe communication device 30, receives the high frequency alternatingcurrent power from the communication device 30.

The power receiving circuit 53 receives, via the antenna 52, the highfrequency alternating current power output from the loop-shaped antenna63. That is, the communication device 50, which is directly coupled withthe communication device 30, receives the high frequency alternatingcurrent power from the communication device 30.

As described above, even when a disconnection occurs in the power line60, the communication device 30 is able to supply the high frequencyalternating current power to other communication devices 40, 50.

In the foregoing embodiment, the communication system 1 includes thecommunication device 10, the communication device 20, the power line 60,and the communication devices 30, 40, 50. The communication device 10outputs the high frequency alternating current power via the antenna 12.The communication device 20 has the power receiving circuit 23 thatreceives, via the antenna 22, the high frequency alternating currentpower output from the antenna 12. The power line 60 is connected betweenthe antenna 22 and the power receiving circuit 23. The power line 60includes the first power line and the second power line. The first powerline is connected between the intermediate portion 60 a of the powerline 60 and the antenna 22, and includes the semicircle portions 61 a,62 a, 63 a. The second power line is connected between the intermediateportion 60 a of the power line 60 and the power receiving circuit 23,and includes the semicircle portions 61 b, 62 b, 63 b. A combination ofthe semicircle portions 61 a and 61 b configures the loop-shaped antenna61. A combination of the semicircle portions 62 a and 62 b configuresthe loop-shaped antenna 62. A combination of the semicircle portions 63a and 63 b configures the loop-shaped antenna 63. The communicationdevices 30, 40, 50 receive the high frequency alternating current poweroutput from the respective loop-shaped antennas 61, 62, 63 viarespective antennas 32, 42, 52. The communication device 10 isconfigured to transmit or receive communications signals to or from eachof the communication devices 20, 30, 40 via a corresponding antenna. Inthe power line, a portion other than the loop-shaped antennas 61, 62, 63configures a twisted line pair (twisted pair structure) in which thefirst power line is twisted with the second power line as a pair.

The twisted line pair is a cable in which the first power line and thesecond power line are twisted with each other. Thus, the magnetic fieldgenerated by the first power line and the magnetic field generated bythe second power line are compensated by each other. Thus, in the powerline 60, a leakage of the high frequency alternating current power andthe communication signals from a portion other than the loop-shapedantenna 61 can be suppressed.

In the present embodiment, the frequency of the high frequencyalternating current power is set equal to a resonance frequency of thecommunication system 1. Thus, in the power line 60, a leakage of thehigh frequency alternating current power from the portion other than theloop-shaped antenna 61 can be further suppressed.

In the present embodiment, the communication devices 30, 40, 50 transmitor receive the high frequency alternating current power and thecommunication signals to or from the power line 60 in a wireless manner.Thus, connecting elements, such as connectors, are not required forconnecting each of the communication devices 30, 40, 50 with the powerline 60.

The following will describe a space transfer efficiency K·Q between theloop-shaped antenna 61, 62, 63 and the corresponding antenna 32, 42, 52of the communication device 30, 40, 50 with reference to FIG. 3, FIG. 4,FIG. 5A, and FIG. 5B.

FIG. 3 is a graph showing a relation between the space transferefficiency K·Q on the vertical axis and a radius R of the loop-shapedantenna 61 on the horizontal axis (in the figure, illustrated as loopradius R as shown in FIG. 5B).

The space transfer efficiency K·Q is a parameter showing an efficiencyof power transfer from the loop-shaped antenna 61 (62, 63) to theantenna 32 (42, 52).

When the radius R of the loop-shaped antenna 61 is within a range of 1.5mm to 4.5 mm and the radius r of the antenna 32 (receiving coil) isequal to 3 mm, the space transfer efficiency K·Q is equal to or higherthan 50%. That is, when the radius R of the loop-shaped antenna 61 iswithin a range of 0.5xr to 1.5xr, the space transfer efficiency K·Q isequal to or higher than 50%. On the other hand, when the radius R of theloop-shaped antenna 61 is out of the range of 0.5xr to 1.5xr, the spacetransfer efficiency K·Q is lower than 50%.

The radius r of the antenna 32 is a radius of a cross section of theantenna 32. Herein, the cross section of the antenna 32 is perpendicularto an axis direction of the antenna 32.

A relation between the radius R of the loop-shaped antenna 62, 63 andthe space transfer efficiency K·Q thereof is similar to the relationbetween the radius R of the loop-shaped antenna 61 and the spacetransfer efficiency K·Q thereof.

An amount of the high frequency alternating current power transferredfrom the loop-shaped antenna 61 (62, 63) to the antenna 32 (42, 52) isdefined corresponding to a dimension of the loop-shaped antenna 61 (62,63).

FIG. 4 is a graph showing a relation between a space transfer efficiencyK·Q on the vertical axis and a distance g (refer to FIG. 5A) on thehorizontal axis. As shown in FIG. 5A, the distance g is a distancebetween the loop-shaped antenna 61 and the antenna 32 (receiving coil).

When the distance g is equal to or shorter than 6 mm and the radius r ofthe cross section of the antenna 32 (receiving coil) is equal to 3 mm,the space transfer efficiency K·Q is equal to or higher than 50%. Thatis, when the distance g is equal to or shorter than 2xr (twice of radiusr), the space transfer efficiency K·Q is equal to or higher than 50%.When the distance g is longer than 2xr, the space transfer efficiencyK·Q is lower than 50%.

A relation between the distance g related to the loop-shaped antenna 62,63 and the space transfer efficiency K·Q thereof is similar to therelation between the distance g related to the loop-shaped antenna 61and the space transfer efficiency K·Q thereof.

An amount of the high frequency alternating current power transferredfrom the loop-shaped antenna 61 (62, 63) to the antenna 32 (42, 52) isalso defined corresponding to the distance g.

As described above, the amount of the high frequency alternating currentpower transferred from the loop-shaped antenna 61 (62, 63) to theantenna 32 (42, 52) of the corresponding communication device is definedaccording to the dimension of the loop-shaped antenna 61 (62, 63) andthe distance g between the loop-shaped antenna and the antenna of thecorresponding communication device. Thus, when the consumption power ofeach communication device 30, 40, 50 is different from one another, theamount of the high frequency alternating current power required by eachcommunication device 30, 40, 50 can be appropriately set according tothe electric load of each communication device 30, 40, 50 by adjustingthe dimension of the loop-shaped antenna and the distance g. Thus, anexcessive power supply to the communication device 30, 40 50 can besuppressed. Accordingly, there is no need to dispose an overcurrentprotection structure in each communication device 30, 40, 50.

In FIG. 5A and FIG. 5B, symbol C1 indicates a capacitor that configuresa part of the antenna 12. The symbol C2 indicates a capacitor thatconfigures a part of the antenna 22. In the present embodiment, a pitchof the twisted line pair is set to 12.5 (mm).

Other Embodiments

In the foregoing embodiment, the communication system is applied to thevehicle. As another example, the communication system may be applied toa different equipment other than the vehicle. For example, thecommunication system may be applied to a household equipment.

In the foregoing embodiment, the communication device 10 operates as themaster, and the communication devices 20, 30, 40, 50 operate as slaves,and the communication system operates in a master-slave manner. Asanother example, in the communication system, the communication devices10, 20, 30, 40, 50 may operate in a different manner other than themaster-slave manner.

In the foregoing embodiment, the communication device 10 performscommunication with the communication devices 20, 30, 40, 50 as anexample. As another example, any two of the communications devices 10,20, 30, 40, 50 may perform communication with each other. That is, anytwo of the communications devices 20, 30, 40, 50 may performcommunication with each other.

In the foregoing embodiment, the antennas 12, 22, 32, 42, 52 areprovided by the coil-shaped antennas. As another example, the antennas12, 22, 32, 42, 52 may be provided by different types of antennas (forexample, loop-shaped antenna) other than the coil-shaped antennas.

In the foregoing embodiment, the power line 60 includes threeloop-shaped antennas (61, 62, 63) as an example. As another example, thepower line 60 may include only one loop-shaped antenna, or twoloop-shaped antennas. As another example, the power line 60 may includefour or more loop-shaped antennas.

The communication device 10 corresponds to a first communication device,and the antenna 12 corresponds to a first antenna. The communicationdevice 20 corresponds to a second communication device, and the antenna22 corresponds to a second antenna. The communication device 30corresponds to a third communication device, and the antenna 32corresponds to a third antenna. The communication device 40 or 50corresponds to a fourth communication device, and the antenna 42 or 52corresponds to a fourth antenna.

While the disclosure has been described with reference to preferredembodiments thereof, it is to be understood that the disclosure is notlimited to the preferred embodiments and constructions. The disclosureis intended to cover various modification and equivalent arrangements.In addition, while the various combinations and configurations, whichare preferred, other combinations and configurations, including more,less or only a single element, are also within the spirit and scope ofthe disclosure.

What is claimed is:
 1. A communication system comprising: a firstcommunication device including a first antenna, the first antennaoutputting a high frequency alternating current power; a secondcommunication device including a second antenna and a power receivingcircuit, the power receiving circuit receiving, via the second antenna,the high frequency alternating current power output from the firstantenna; a power line connected between the second antenna and the powerreceiving circuit, wherein the power line includes a first power line,which is positioned between a predetermined portion of the power lineand the second antenna, and a second power line, which is positionedbetween the predetermined portion of the power line and the powerreceiving circuit, the first power line includes at least one firstsemicircle portion having a semicircle shape and the second power lineincludes at least one second semicircle portion having a semicircleshape, the at least one first semicircle portion and the at least onesecond semicircle portion being combined together to provide at leastone loop-shaped antenna; and a third communication device including athird antenna, the third communication device receiving, via the thirdantenna, the high frequency alternating current power output from the atleast one loop-shaped antenna, wherein at least two of the firstcommunication device, the second communication device, or the thirdcommunication device transmit or receive communication signals viacorresponding antennas, and the first power line and the second powerline are twisted with each other to configure a twisted line pair at aportion other than the at least one loop-shaped antenna in the powerline.
 2. The communication system according to claim 1, wherein afrequency of the high frequency alternating current power is set equalto a resonance frequency of the communication system.
 3. Thecommunication system according to claim 1, wherein an amount of the highfrequency alternating current power that is transferred from the atleast one loop-shaped antenna to the third antenna is defined accordingto a distance between the at least one loop-shaped antenna and the thirdantenna and a dimension of the at least one loop-shaped antenna.
 4. Thecommunication system according to claim 3, wherein the third antenna isa coil-shaped antenna.
 5. The communication system according to claim 4,wherein a radius of the at least one loop-shaped antenna is equal to orlonger than a half of a radius of the third antenna and equal to orshorter than one and a half of the radius of the third antenna.
 6. Thecommunication system according to claim 5, wherein the distance betweenthe at least one loop-shaped antenna and the third antenna is equal toor shorter than twice of the radius of the third antenna.
 7. Thecommunication system according to claim 1, further comprising a fourthcommunication device including a fourth antenna, wherein the first powerline includes at least two first semicircle portions and the secondpower line includes at least two second semicircle portions, one of theat least two first semicircle portions is combined with a correspondingone of the at least two second semicircle portions to provide a firstloop-shaped antenna, another one of the at least two first semicircleportions is combined with corresponding another one of the at least twosecond semicircle portions to provide a second loop-shaped antenna, thethird communication device is positioned corresponding to the firstloop-shaped antenna and the fourth communication device is positionedcorresponding to the second loop-shaped antenna, and the fourth antennareceives, via the fourth antenna, the high frequency alternating currentpower output from the second loop-shaped antenna.
 8. The communicationsystem according to claim 7, wherein the third communication devicefurther includes a power storage circuit that stores an electric powerbased on the high frequency alternating current power received via thethird antenna.
 9. The communication system according to claim 8, whereinthe third communication device further includes: a power transfercircuit transferring, based on the electric power stored in the powerstorage circuit, a high frequency alternating current power to the firstloop-shaped antenna via the third antenna; and a disconnection detectioncircuit detecting a disconnection of the power line between the firstloop-shaped antenna and the second antenna, wherein, when thedisconnection detection circuit detects the disconnection of the powerline between the first loop-shaped antenna and the second antenna, thedisconnection detection circuit controls the power transfer circuit tooutput the high frequency alternating current power to the firstloop-shaped antenna via the third antenna, and the fourth communicationdevice receives the high frequency alternating current power from thesecond loop-shaped antenna, the high frequency alternating current poweris output from the power transfer circuit of the third communicationdevice to the first loop-shaped antenna and is transferred to the secondloop-shaped antenna via the power line.
 10. The communication systemaccording to claim 1, wherein at least one of the first antenna or thesecond antenna is a coil-shaped antenna.